Field of the Invention
The present invention generally relates to a photocatalytic structure, in particular to a photocatalytic film containing titanium dioxide with shape of rhombus particles.
Description of Related Art
Photocatalysts are materials in which, when exposed to light, electron-hole pairs are formed that generate highly reactive free radicals on the material surface. Titanium dioxide is a material of this kind, and most frequently used to make photocatalysts due to high oxidizing ability, high chemical stability and non-toxic property thereof. It is known practice to use photocatalysts to remove harmful chemicals with low concentration in the air without releasing harmful materials. Therefore, photocatalysts are excellent catalysts used in environmental clean-up application. Photocatalysts have antibacterial, deodorizing and stainproofing functions and the use of removing harmful substances. However, the antibacterial effect of photocatalysts under ultraviolet light at wavelength of 365 nm is limited, and the antibacterial effect of photocatalysts cannot be exhibited without UV light.
There are three kinds of titanium dioxide crystallic structures with rutile type and anatase type of tetragonal system, and brookite type of rhomic system, in which only titanium dioxide with the anatase type has photocatalytic effect. The principle of photocomposition of photocatalysis is described. Titanium oxide has the property of absorbing ultraviolet light at wavelengths below approximately 400 nm or sunlight and producing an excited electron. When the generated electron and hole reach the particle surface, combinations with oxygen and water and the like generate a variety of different radicals. These radicals typically cause an oxidizing action, and oxidize and decompose substances adsorbed to the surface thereof. The use of the optical functions of ultrafine particles of titanium oxide in antibacterial, deodorizing and stainproofing applications, and in environmental clean-up applications such as atmospheric purification and water quality purification are currently under investigation.
A powdery titanium dioxide can be added into waste water directly to decompose organic substances therein, or coated on the surface of a carrier to decompose organic substances in the air by exposing to UV light. However, those methods have problems such that it is troublesome to recycle the powdery titanium dioxide, and a part of surface area of the photocatalyst cannot be irradiated by UV light. In order to solve those problems, a titanium dioxide film can be used to increase the surface area that may be exposed to UV light, and thus the effect of photocatalysis can be increased.
Conventionally, titanium dioxide with shape of sphere particles has been used as a photocatalyst. However, a photocatalytic film which is formed by titanium dioxide with shape of sphere particles has a poor overall photocatalytic activity. Because the space formed among the sphere particles is large, less amount of titanium dioxide with shape of sphere particles can be contained in a unit of volume. Also, titanium dioxide with shape of sphere particles has a poor photocatalytic activity. Therefore, there is a need to enhance the properties of the photocatalytic film.